The present invention concerns a receiving system for the post-treatment of a hollow body molding produced in an injection molding mold, and a corresponding method.
Moldings or preforms of plastic materials are produced in large numbers using injection molding methods. Particular significance is attributed to the production of hollow body moldings, referred to as preforms, of PET (polyethylene terephthalate), as the foundation for the production of PET drinks bottles. After the injection molding procedure is concluded the hollow body moldings are inflated to the desired final dimension at the same location or another location by blow molding.
Injection molding machines having tools which have a large number of mold cavities, for example 48, are used for injection molding of the hollow body moldings. Therefore at the moment up to 192 moldings can be produced in parallel in respect of time during a single injection molding cycle. As the number of mold cavities is subjected to a limit by virtue of the limited spatial dimensions of the closure units of injection molding machines, the cycle time, that is to say the time required to produce a molding in a mold cavity, must be shortened to provide an increase in the number of moldings which can be produced in a time interval. In that respect the procedure adopted has been to remove the moldings from the injection molding mold progressively earlier within the injection molding cycle in order to be able to use the mold for the next injection step. In spite of cooling the individual mold cavities the moldings, at earlier moments of removal of the moldings from the mold cavities, have still not cooled down to such an extent that they can be removed without the risk of deformation. Admittedly the moldings are externally cooled down to such a degree that they have a stable outside contour, but the plastic material in the interior of the moldings is still fluid. If the dissipation of heat from the surface of the moldings is interrupted, the plastic material at the surface of the moldings also liquefies again by virtue of the transport of heat out of the interior of the moldings to the surface. Therefore, in the removal operation and in the immediately subsequent phase, care must be taken to provide that the moldings do not experience any deformation and the moldings are further cooled subsequently to removal thereof from the mold cavities.
Further cooling and thus complete hardening of the moldings is then effected outside the actual mold cavities and outside the closure unit so that they are available for the next injection molding operation.
The tools known from the state of the art for preforms for the production of bottles are so arranged that the mold cavities are filled from the closed end of the moldings. In that way the feedhead for the bottles is disposed on the one hand in the bottom region of the bottle which is not directly visible to the end consumer, while on the other hand the oppositely disposed end of the preform, that is to say the bottle neck with the screwthread, is extremely critical in terms of dimensional accuracy so that no further post-treatment is effected after the injection molding operation at that end.
The individual mold cavities for the preforms comprise generally at least three parts: a cavity which forms the outside shape for the belly portion of the preform, a neck jaw which is in two parts and which in the closed condition forms the mold for the neck, that is to say generally for the screwthread as well as the carrying ring and the sealing ring of the bottle, and a core which defines the inside surface of the preform.
In order to remove the finished hollow body molding from the mold cavity, the molding together with the core is usually withdrawn from the cavity forming the outside shape of the preform, in which case the neck jaw is closed so that it holds the molding on the core. The removal plate is then moved with a removal sleeve or cavity into the region under the molding, while in a further step the neck jaw, that is to say the mold for the bottle neck, is opened by laterally moving the two halves into the open position so that the molding can slip off the core of the mold and drops into the removal cavity or is moved thereinto by means of a compressed air pulse. After the removal plate has been removed from the closure unit the tool is available for the next injection molding operation. If the tool has a plurality of mold cavities a corresponding number of removal cavities is provided in the removal plate.
The foregoing description relates to what is known as a vertical system in which the closure unit closes in a vertical direction. Therefore the mold cavities also extend substantially in a vertical direction so that the force of gravity can be used for withdrawing the moldings from the cores. As an alternative thereto there are also horizontal systems, the closure units of which close in a horizontal direction. In that case the mold cavities also extend substantially horizontally. In horizontal systems therefore the moldings are frequently withdrawn from the core by means of additional forces, for example by compressed air or by a mechanical gripper.
A post-treatment of the molding takes place in the removal cavity, that is to say it is cooled down here until it has reached its entire stability and a glass-like, that is to say transparent and clear, structure for the molding can be guaranteed.
The state of the art, in particular U.S. Pat. No. 6,475,422 B1, also discloses removal systems in which, in addition to cooling of the removal cavity, a cooling finger is introduced into the interior of the molding, the cooling finger cooling the molding from its inside by means of an air flow. In that case contact with the inside of the molding is avoided in order not to constitute any further sources of deformation.
In the removal systems known from the state of the art, the cooling effect is transmitted to the moldings only to a limited degree as, by virtue of shrinkage of the PET material when cooling occurs, there is only imperfect contact between the removal cavity and the molding.
In addition the neck region of the hollow body molding cannot be cooled in thermal contact with the cavity by virtue of undercut configurations due to the screwthread and the neck ring, but only by a complicated and expensive air shower effect, that is to say by guiding an air flow past the outside of the neck of the molding.